MANCHESTER, N.H. — Vermont Sen. Bernie Sanders (I) and New Jersey Gov. Chris Christie (R) on Monday offered strikingly different plans to extend the life of Social Security, a charged topic other 2016 presidential candidates have largely avoided.

Sanders, one of the program’s most vocal defenders in the Senate, laid out his plan to boost it by eliminating the cap on the payroll tax on income above $250,000.

He wants to use the new revenue to expand benefits, saying it would extend the life of the system to the year 2061.

Speaking via video feed to the Problem Solvers Convention sponsored by No Labels and The Hill, he argued that the fairest way to extend the life of Social Security over the next 50 years is to make sure the nation’s wealthiest earners pay the same percentage of their income to Social Security as middle-class families. 

“Somebody who is making hundreds and hundreds of millions of dollars a year pays the same amount of money into the Social Security trust fund as somebody who makes $118,500 a year. In my view, that is wrong,” he said.

Christie, by contrast, says giving the federal government more money to fix Social Security is a fool’s errand.

Appearing in person before a bipartisan crowd immediately before Sanders spoke, he called for raising the retirement age from 67 to 69, phasing in the change over 25 years.

He touted himself as the only candidate in the Republican presidential primary willing to propose a detailed plan to reform Social Security, which would become a target in the general election if he won the nomination.

“That would be one month in increase in eligibility in a year for 25 years. Believe me, the world will not stop spinning on its axis because of this,” he said.

Christie also wants to stop paying benefits to retirees with millions of dollars in savings.

He recounted a conversation with Facebook founder Mark Zuckerberg, who is worth an estimated $35 billion, who asked about his plan for the safety-net program.

“I said, ‘What it means for you, Mark, is you get nothing. You get absolutely nothing. You’re going to get zero, brother. You don’t need it and you don’t get it,’” he said.

He argued that politicians in Washington have already raided the Social Security trust fund to make up for shortfalls in the general fund and that giving them more revenue wouldn’t necessarily help the program.

No Labels, a social welfare advocacy group, is pressing candidates to focus on four major policy goals, including securing Social Security and Medicare for another 75 years.

Sanders and Christie clashed over the projected financial health of the program.

Sanders cited a Social Security Administration estimate that it can pay out every benefit owed to every eligible American over the next 19 years.

Christie says the outlook is much more dire.

“In seven to eight years, Social Security is not going to be able to make the payments they make now,” he said. “Take that in for a second. Seven to eight years. A Harvard-Dartmouth study just came out a few months ago [and] said Social Security will be insolvent.”

Sanders later dismissed that claim as inaccurate. 

“Social Security is not going broke. I know everyday on television somebody is saying Social Security is going broke. 'We’ve got to cut Social Security. We’ve got to raise the retirement age.' That is simply not accurate,” he insisted.